Electrophysiological cardiac mapping system based on a non-contact non-expandable miniature multi-electrode catheter and method therefor

ABSTRACT

A system ( 10 ) for determining electrical potentials on an endocardial surface of a heart is provided. The system includes a non-contact, non-expandable, miniature, multi-electrode catheter probe ( 12 ), a plurality of electrodes ( 32 ) disposed on an end portion ( 30 ) thereof, means for determining endocardial potentials ( 14 ) based on electrical potentials measured by the catheter probe, a matrix of coefficients that is generated based on a geometric relationship between the probe surface, and the endocardial surface. A method is also provided.

This application is a 371 of PCT/US98/15712, Jul. 29, 1998 which claimsbenefit of provisional application Ser. No. 60/054,342 filed Jul. 31,1997.

This research is supported by the National Institutes of Health, GrantNo. 2 RO1 HL-33343 (Sponsor: NIH-NHLRI).

BACKGROUND OF THE INVENTION

This invention relates to an apparatus and method forelectrophysiological cardiac mapping. More particularly, the inventionis directed to a system based on a nonexpandable, noncontact, miniature,multielectrode catheter which is used to measure electrical potentialswithin a heart cavity. These measured potentials are then used, alongwith data on the geometric relationship between the catheter and theendocardial surface, to reconstruct maps representing endocardialelectrical activity. In this regard, electrograms and isochrones arereconstructed.

While the invention is particularly directed to the art ofelectrophysiological cardiac mapping, and will be thus described withspecific reference thereto, it will be appreciated that the inventionmay have usefulness in other fields and applications.

By way of background, endocardial potential mapping is a tool forstudying cardiac excitation and repolarization processes. Mappingendocardial potential distribution and its evolution in time is usefulfor analyzing activation and repolarization patterns and for locatingarrhythmogenic sites and regions of abnormal electrical activity in theheart. Accurate localization of arrhythmogenic sites is important to thesuccess of non-pharmacological interventions, such as catheter ablation.

Unfortunately, current techniques of mapping potentials directly fromthe endocardium present certain difficulties. For example, thewell-known “roving” probe approach is 1) limited in the number ofrecording sites, 2) too time consuming and 3) only operative to collectdata over a plurality of heart beats, instead of a single beat.Therefore, this approach is not useful on a beat-by-beat basis to studydynamic changes in the activation process.

In addition, multiple electrode balloons or sponges have also been usedto map electrical activity of the heart by way of measuring potentialswithin a heart cavity. Although capable of mapping the entireendocardium, these devices occlude the heart cavity and require openheart surgery, heart-lung bypass and other complicated and high riskprocedures.

Another device having a multiple-spoke, basket-shaped recording catheterallows simultaneous acquisition of potential data from multipleelectrodes without occluding the cavity. However, the basket isnonetheless limited in the number of electrodes so that spatialresolution is relatively low. Moreover, it is difficult to insure thatall electrodes make contact with the endocardium. Also, the basket canbe entangled in intracavitary structures such as the chordae tendineae.The fact that the basket must be collapsed prior to catheter withdrawalfrom the ventricle adds complexity and risk to this procedure.

Still another known device for detecting endocardial potentials uses anelectrode array catheter that can be expanded within the heart chamberbut does not occlude the heart chamber. However, this system stillinvolves undesirable expansion of a device in the heart chamber. Theexpanded element may interfere with intracavity structures and addscomplexity to the system because it must be collapsed before removal.Moreover, it is difficult to determine the location of the electrodeswithin the chamber. Also, the array may not expand as desired, leadingto inaccuracies in mapping.

Taccardi et al. developed an alternative indirect mapping approach thatmakes use of a large (too large for clinical applications) intracavitarymultielectrode catheter-probe (olive shaped or cylindrical), that can beintroduced into the blood filled cavity without occluding it. The probepermits simultaneous recording of intracavitary potentials from multipledirections but, unlike the balloon, is not in direct contact with theendocardium and does not record actual endocardial potentials. Theintracavitary probe potentials exhibit smoothed-out distributions and donot reflect details of the excitation (or repolarization) process thatcan be detected and located by direct endocardial recordings. It ishighly desirable, therefore, to develop an approach for reconstructingendocardial potentials, electrograms and isochrones from data recordedwith a small, non-expanding intracavitary catheter-probe that can beintroduced percutaneously, does not occlude the ventricle, and/or doesnot require opening large structures (e.g. basket or balloon) inside thecavity.

Accordingly, it would be desirable to have available a multielectrodecatheter probe that can be introduced percutaneously, without expandinginside the ventricular cavity, and provide accurate reconstructedendocardial potentials, electrograms and isochrones.

The present invention contemplates a new and improved system and methodfor electrophysiological cardiac mapping using a non-contact,non-expandable catheter which resolves the above referenced difficultiesand others and attains the above referenced desired advantages andothers.

SUMMARY OF THE INVENTION

A system for determining electrical potentials on an endocardial surfaceof the heart is provided. In one aspect of the invention, the systemcontains a noncontact, non-expandable, miniature catheter probe that ispercutaneously positioned inside a heart cavity. A plurality ofelectrodes are disposed on an end portion of the probe wherebyelectrical potentials within the heart cavity are measured. Alsoincluded is a means for generating a matrix of coefficients which isthen used along with the electrical catheter potentials to determineendocardial potentials.

In a further aspect of the invention, the probe assumes a curved shapeinside the cavity.

In a further aspect of the invention, the system includes means forgenerating electrograms and isochrones based on the determinedendocardial potentials.

In a further aspect of the invention, the curved shape of the terminalend of the electrode catheter resembles a “J”, “U”, “O”, helix, pigtail,or any general curved shape.

In a further aspect of the invention, the system includes a means forconforming the terminal end portion of the probe to the first elongatedshape and a means for conforming the terminal end of the end portion ofthe probe into the second curved shape.

In a further aspect of the invention, a method for implementing thesystem is provided.

Further scope of the applicability of the present invention will becomeapparent from the detailed description provided below. It should beunderstood, however, that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art.

DESCRIPTION OF THE DRAWINGS

The present invention exists in the construction, arrangement, andcombination of various parts of the device and steps of the methods,whereby the objects contemplated are attained as hereinafter more fullyset forth, specifically pointed out in the claims, and illustrated inthe accompanying drawings in which:

FIG. 1(a) is a representative illustration of the system according tothe present invention;

FIG. 1(b) is an illustration of the catheter according to the presentinvention positioned within a heart cavity;

FIG. 2 is a side view of an end portion of a catheter probe according tothe present invention having a first shape;

FIG. 3 is a side view of the end portion of the catheter probe accordingto the present invention having a second shape;

FIGS. 4(a)-(e) are side views of the end portion of various catheterprobes according to the present invention having another second shape;

FIG. 5(a) is a functional block diagram of the processor according tothe present invention;

FIG. 5(b) is a flow diagram illustrating a software tool implementedaccording to the present invention;

FIG. 6 is a flow chart showing the method according to the presentinvention;

FIG. 7 is a schematic representing the geometry of a human ventricularcavity containing a probe;

FIG. 8 shows selected sites on the endocardial surface for electrogramdisplay in utilizing the present invention;

FIG. 9 includes electrograms showing results obtained using the presentinvention;

FIG. 10 includes electrograms showing results obtained using the presentinvention;

FIG. 11 includes electrograms showing results obtained using the presentinvention;

FIG. 12 includes isochrone maps showing results obtained using thepresent invention;

FIG. 13 includes isochrone maps showing results obtained using thepresent invention;

FIG. 14 is an illustration explaining geometric and rotational errors;

FIG. 15 includes electrograms showing results obtained using the presentinvention;

FIG. 16 includes isochrone maps showing the effects of probe rotation of5/ on the present invention;

FIG. 17 includes isochrone maps showing the effects of probe rotation of10/ on the present invention;

FIG. 18 includes isochrone maps showing the effects of probe rotation of5/ and 10/ on the present invention;

FIG. 19 includes electrograms showing the effects of probe shift on thepresent invention;

FIG. 20 includes isochrone maps showing the effects of probe shift onthe present invention;

FIG. 21 includes isochrone maps showing the effects of probe shift onthe present invention;

FIG. 22 includes electrograms showing the effects of twisting on thepresent invention;

FIG. 23 includes isochrone maps showing the effects of twisting on thepresent invention;

FIG. 24 includes electrograms showing the effects of catheter probeshape on the present invention;

FIG. 25 includes isochrone maps showing the effects of catheter shape onthe present invention;

FIG. 26 includes isochrone maps showing the effects of catheter shape onthe present invention;

FIG. 27 includes isochrone maps showing the effects of catheter shape onthe present invention;

FIG. 28 includes isochrone maps showing the effects of catheter shape onthe present invention;

FIG. 29 includes measured and computed potential maps; and,

FIG. 30 includes measured and computed potential maps.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A mathematical inverse methodology for reconstruction of endocardialpotentials, electrograms and isochrones from non-contact, intracavitaryprobe measurements has been developed and validated. A study in anisolated canine left ventricle (LV) demonstrated that the inverselycomputed endocardial potential maps reconstruct with good accuracy andresolve the major features of the measured endocardial potential maps,including maxima, minima and regions of negative and positivepotentials. A more recent systematic evaluation demonstrated thatcomputed temporal electrograms and isochrones also closely approximatetheir directly measured counterparts. The isochronal maps correctlycaptured the regions of early and late activation for a single pacingsite and for two simultaneous pacing sites separated by 17 mm. Moreover,the entire activation sequence was closely approximated, includingregions of nonuniform conduction (e.g. isochrone crowding indicatingslow conduction). The size of the probe, though, was too large forclinical application.

The reconstruction methodology can be adapted to the clinicalenvironment with two additional developments: (1) reduction in size ofthe intracavity multielectrode probe; and (2) noninvasive determinationof the geometric relationship between the probe and the endocardium. A9-French (3-mm) multielectrode catheter that can be introducedpercutaneously has been developed. The present invention demonstratesthat endocardial potentials can be reconstructed from a 3-mm cylindricalprobe with accuracy.

In the experiments (the results of which are outlined herein withreference to FIGS. 8-30), the geometry of the endocardium was determinedinvasively after completion of the potential measurements. The abilityto measure the geometry directly improved accuracy. However, the factthat the geometry was not obtained at the time of potential measurementsintroduced an error, since myocardial changes upon termination ofperfusion changed somewhat the positions of the intramural needles.Moreover, all computations assumed a single cavity geometry(end-diastolic volume) throughout the experiment, whereas the degree ofblood filling varied between pacing protocols and between time framesduring a given protocol. The probe positions/orientation within thecavity was estimated using an automated optimization procedure and wassubject to error as well.

Nonetheless, the experiments confirm that, in spite of geometry errors,electrograms and isochrones can be reconstructed over the entireendocardium with good accuracy. This property is useful in terms ofclinical application of the approach.

As will be described below, existing noninvasive imaging techniques,such as ultrasound, can provide the endocardial geometry and probeposition simultaneously and at the time of potential measurements. Thisconstitutes an improvement over the method used in the experiments. Thegeometric robustness of the reconstruction procedure implies that itcould be combined with a noninvasive imaging modality (high accuracy canbe achieved with transesophageal echocardiography for example) toreconstruct endocardial potentials, electrograms, and isochrones on abeat-by-beat basis in the clinical catheterization laboratory.

Referring now to the drawings wherein the showings are for purposes ofillustrating the preferred embodiments of the invention only and not forpurposes of limiting same, FIG. 1(a) provides a view of the overallpreferred embodiment. As shown, the system 10 includes a catheter probe12—which is positioned in a cavity of the heart H by well knownmethods—a processor (or computer) 14, an imaging (or geometrydetermining) device 16, an output device 18 (which may take the form ofa display (as shown), or a printer or other suitable output device), anda mechanism 20 for steering and manipulating an end portion of catheterprobe 12. FIG. 1(b) shows the catheter 12 (shown in an exemplary curvedshape) positioned in the heart H.

The end portion 30 of catheter probe 12, as shown in FIG. 2, isgenerally cylindrical in cross section and has disposed thereon aplurality of electrodes, exemplary shown at 32. It should be noted thatherein, like numerals in the drawings indicate like elements.Preferably, the catheter probe is a 9-French (9F), 3.0 mm catheter;however, any usable style and size will suffice. For clinicalapplications, of course, the catheter is preferably of a size tofacilitate percutaneous introduction into the cavity. The number ofelectrodes may vary depending on the needs of the particularapplication. Of course, varying the number of electrodes consequentlyimpacts the results obtained using the invention, as will be moreparticularly described hereinafter.

As illustrated in FIG. 3, the end portion of the catheter probe 12 maybe conformed to a curved shape of FIG. 3 once positioned in the heartcavity. As shown, the exemplary shape is that of a “J”. It should beemphasized that the label “J” (and other similar labels) refers to theend portion of the catheter that has electrodes disposed thereon, notthe entire catheter. The end portion is conformed to this shape by knownmethods and the mechanism 20 represented generally in FIG. 1, as thoseskilled in the art will appreciate.

Of course, the precise shape of the end portion 30 of the catheter probe12 may be varied to suit a particular application of the catheter probe.For example, the end may be conformed to a “U,” “O”, pigtail, helix orany known curve. As is shown in FIG. 4(a), the exemplary “U” shapedcatheter end portion shape is shown whereby the end portion is furthermanipulated from the J-shape to resemble a “U”. The angle of curvatureis preferably the same as that of the J-shaped configuration but it isrecognized that the angle of curvature may be varied without affectingthe scope of the invention. FIGS. 4(b)-(e) show curved catheters havingend portions conformed to an “O”, a pigtail, a helix, and a generalrepresentative curve, respectively. It should be appreciated thatvarying the shape of the end portion of the catheter probe impacts theresults obtained using the invention, as will be more particularlydescribed hereinafter but, importantly, the invention and resultant testdata indicate that a noncontact, nonexpandable, miniature multielectrodecatheter probe of any shape or configuration (including straight) isuseful for cardiac mapping.

Referring now to FIG. 5(a), functional blocks of the processor 14 aredescribed. Those skilled in the art will appreciate that the processor14 actually includes suitable software and hardware (including, forexample, memories) that accomplish the functions described. In oneembodiment, the software tool implemented takes the general form of thatdescribed in connection with FIG. 5(b), although neither the processornor the tool is so limited. For example, it should be recognized thatthe software tool of FIG. 5(b) has features involving testing andvalidation which are not specifically described in connection with FIG.5(a) but would be apparent to those of skill in the art.

Specifically, as shown in FIG. 5(a), data on geometry of the endocardiumand probe are input to the processor 14 from the imaging device 16. Suchdata may be generated using existing imaging modalities such as x-ray,ultrasound, computed tomography (CT), magnetic resonance imaging (MRI),. . . etc. Preferably, the invention is implemented using bi-plane x-raytechniques enhanced with fluoroscopy. These techniques result indetermination of a geometric envelope that approximates the heartchamber.

As is shown in FIG. 5(a), at least one of these known imaging routinesis available to provide data to determine a geometric relationship ofthe endocardial surface (or envelope) and probe surface (block 141)based on the input of the imaging device 16. A matrix of coefficients A,described in more detail below, is also generated (block 142) in theprocessor. In addition, data, i.e. electrical potentials measured in theheart cavity, is input to the processor from the probe 12. These dataare stored in the processor (block 143). Endocardial potentials may thenbe determined by the processor based on the stored electrical potentialsand the matrix of coefficients (block 144). Electrograms and isochronemaps are also generated for display and evaluation (block 145). Theresults, of course, may be output.

As noted above, the software tool may take the general form of the flowdiagram illustrated in FIG. 5(b), but those skilled in the art willappreciate that such a program, which (as will be described) alsoaccommodates testing and validation processes, may well be modifiedand/or evolve into a modified tool (to resemble, for example, only thefeatures described in connection with FIG. 5(a)) as the presentinvention is modified as a result of additional development or needs ofusers. Those skilled in the art will also appreciate that thedescription of this software tool necessarily overlaps with thedescription in connection with FIG. 5(a) because the processor of FIG.5(a) implements such software tools in the described embodiment.

As shown, information is input to the system (step 500). Specifically,parameters are input to the system by the user (step 502). Geometry dataand potential data are also input (steps 504, 506). It should berecognized that in a clinical setting, the geometry data is generated byimaging device 16 and potential data is generated by catheter probe 12;however, if the software tool is implemented for testing and validationpurposes, the geometry data may be known parameters, such as thoseassociated with geometric spheres and torso tanks (used in testing),that are simply input to the system. The overall control program isimplemented (step 508) and it is determined whether to use the softwaretool for testing and validation (using sphere or torso tank data (steps510, 512)) or clinical application (using clinical data (step 514)).Appropriate processing is then conducted on the data (steps 516, 518 or520), as will be apparent to those skilled in the art, to prepare thedata for necessary mathematical manipulation.

Next, a boundary element method (further described below) is applied(step 522). At that time, forward (step 524) or inverse (step 526)computations, as necessary, are performed. Of course, for clinicalapplications, only inverse computations (as described below) are used.Once the data is computed, processing of the data for output isaccomplished (step 528).

Referring now to FIG. 6, the overall method 600 by which endocardialpotentials (and electrograms and isochrones) may be determined accordingto the present invention is described. Initially, a probe 12 ispercutaneously positioned in the cavity of a heart by known methods(step 602). If desired, the end portion of the probe is then conformed,utilizing mechanism 20, to a curved shape such as those shown in FIGS. 3and 4(a)-(e) (step 604). It is recognized that conforming the endportion may not be necessary if the results obtained by using thestraight catheter (of FIG. 2, for example) are acceptable. Potentialsare then measured in the cavity (step 606) and stored (step 608).

A geometric relationship between the probe surface and the endocardialsurface (or envelope) is also determined (step 610). The geometry is, ofcourse, determined using the imaging device 16. Based on this data onthe geometric relationship, a matrix of coefficients A is generated(step 612).

Next, endocardial potentials are determined based on the storedpotentials and the matrix of coefficients (step 614). Electrograms andisochrones are then generated by the processor (steps 616 and 618) anddisplayed (step 620). The procedure is then ended (step 622).

The mathematical computations accomplished by the processor 14 involvedin implementing the present invention described above relate to andshould be analyzed by considering “forward” computations, i.e.calculating catheter probe potentials from known endocardial surfacepotentials, and “inverse” computations, i.e. calculating endocardialsurface potentials based on measured probe potentials. Of course, theinverse computation is the computation that is used for implementationof the present invention (e.g. step 614 in FIG. 6), but understandingthe forward computation is also useful.

While various forward and inverse computations are known, thecomputations involved in connection with the present invention are asfollows. More particularly, computation of probe potentials based onmeasured endocardial potentials (the “Forward Problem”) requires solvingLaplace's equation in the cavity volume (Ω) bounded by the probe surface(S_(p)) and the endocardial surface (S_(e)), as illustrated in FIG. 7.

Below is a description of the mathematical formulation. Further detailscan be found in previous publications such as Khoury D S, B. Taccardi,Lux R L, Ershler P R, Rudy Y, “Reconstruction of endocardial potentialsand activation sequences from intracavitary probe measurements,”Circulation, 91:845-863 (1995); Rudy Y, Messinger-Rapport B J, “Theinverse problem in electrocardiography solutions in terms of epicardialpotentials,” CRC Crit Rev Biomed Eng., 16:215-268 (1988); Rudy Y, OsterH S, “The electrocardiographic inverse problem,” CRC Crit Rev BiomedEng., 20:25-46 (1992), Messinger Rapport B J, Rudy Y, “Computationalissues of importance to the inverse recovery of epicardial potentials ina realistic heart-torso geometry,” Math Biosci, 97:85-120 (1989)(published erratum in Math Biosci, 99(1):141 (1990 April)); Oster H S,Rudy Y, “The use of temporal information in the regularization of theinverse problem of a electrocardiography,” IEEE Trans Biomed Eng.,39:65-75 (1992); and Messinger Rapport B J, Rudy Y, “Regularization ofthe inverse problem in electrocardiography. A model study,” Math Biosci,89:79-118 (1988), all of which are hereby incorporated herein by thisreference.

The behavior of potential, V, within Ω is governed by Laplace'sequation:Δ² V =0 in Ω  (1)subject to the boundary conditions:V=V _(P) on a subset of S _(p)  (2)∂V/∂n =0 on S _(p)  (3)where V_(p) is the potential on the probe surface; ∂V/∂n=0 implies thatcurrent cannot enter the nonconducting probe. A well-known BoundaryElement Method (BEM) (See, for example, Brebbia C A, Dominguez J,Boundary elements: An Introductory Course, McGraw-Hill Book Co., NewYork (1989) or Brebbia et al., Boundary Element Techniques. Theory andApplications in Engineering, Springer Verlag, Berlin (1984)) is used tonumerically solve for the potentials in a realistic geometrycavity-probe system. This results in the following equation that relatesthe probe potentials to the endocardial potentials:V _(p) =A·V _(e)  (4)where V_(p) is a vector of probe potentials of order N_(p) (probesurface nodes), V_(e) is a vector of endocardial potentials of orderN_(e) (endocardial surface nodes), and A is an N_(p)×N_(e) matrix ofinfluence coefficients determined by the geometric relationship betweenthe probe surface and the endocardial surface. The intracavitary probepotentials can be calculated from the endocardial potentials usingequation (4). Since the forward computation is a stable and accurateprocess, the computed probe potentials provide an accurate estimate ofcavity potentials measured by an actual probe of the same design and inthe same intracavitary position. This calculation is useful to verifydata that are obtained using the inverse computation.

The matrix A in equation (4) is determined by the geometricalrelationship between the endocardial surface and the probe surface.Specifically, it requires specification of node positions (correspondingto electrode positions) on the probe and node positions on theendocardium. Geometry data, as noted above, is obtained from the imagingdevice 16 which, again, may involve any of the known imaging modalities.Errors in determining the node positions on these two surfaces,especially probe electrodes, may be amplified due to the nature of theinverse procedure and might consequently introduce errors in thereconstructed endocardial potentials. Accordingly, accuratedetermination of geometry is important for implementation.

In order to compute endocardial electrograms and isochrones, endocardialpotential maps are first computed in a quasi-static fashion for everymillisecond throughout the endocardial activation process. Computingendocardial potentials is the first step in computing temporalelectrograms and isochrones. To compute endocardial potentials fromprobe potentials, the relationship between V_(e) and V_(p) establishedin equation (4) must be inverted. However, because of the ill-posednature of the problem (as described in Rudy Y, Messinger-Rapport B J,“The inverse problem in electrocardiography: solutions in terms ofepicardial potentials,” CRC Crit Rev Biomed Eng., 16:215-268 (1988)),one cannot simply invert matrix A to obtain the endocardial potentials(V_(e)) from probe potentials (V_(p)). A Tikhonov regularizationtechnique is used to stabilize the procedure (See, for example, TikhonovA N, Arsenin V Y, “Solution of Ill-Posed Problems,” 27-94, V H Winston &Sons, Washington, D.C. (1977), or Tikhonov et al., “Solutions ofill-posed problems,” (trans. from Russian) Wiley, N.Y. (1977), which areincorporated herein by reference), and the solution for endocardialpotentials is obtained by minimizing the objective function:min/v _(e) [||V _(p) −A·V _(e)||² +t||V _(e)||²]  (5)or, more generally, minimizing||V _(p) −A·V _(e)||² +tF[V _(e)]where t is a regularization parameter, whose optimal value wasdetermined using the CRESO (composite residual and smoothing operator)method (See, Colli-Franzone P, Guerri L, Taccardi B. Viganotti C,“Finite element approximation of regularized solutions of the inversepotential problem of electrocardiography and applications toexperimental data” Calcolo 1985, 22:91-186, and Colli-Franzone et al.,“Mathematical procedure for solving the inverse problem ofelectrocardiography,” Math Biosci, 77:353-96 (1985), which areincorporated herein by reference).

The approach to verifying the accuracy of the data obtained is based ona combination of experimentally measured endocardial potentials andsimulated catheter probes in an isolated LV preparation. The simulatedcatheter data is used to reconstruct endocardial electrograms andisochrones, which are then evaluated by direct comparison with theirmeasured counterparts.

In contrast to potentials, electrograms and isochrones provide completespatio-temporal information for the entire activation cycle. Endocardialelectrograms provide temporal information on activation in localizedareas and are widely used in clinical practice. Isochrones provideextensive spatio-temporal information about the entire activationsequence that can be seen in one glance. Isochronal maps also canidentify spatial nonuniformities of propagation such as regions of slowconduction or areas of conduction block that are important mechanisticproperties of arrhythmogenic activity. Therefore, it is useful toevaluate the accuracy with which electrograms and isochrones can bereconstructed from the noncontact catheter. Single-site pacing protocolsas well as simultaneous dual-site pacing were employed. Becauseelectrograms and isochronal maps contain temporal information from theentire cardiac cycle, their accurate reconstruction places moredemanding design criteria on the catheter probe. The results belowdemonstrate that, as in the case of potential reconstruction,endocardial electrograms and isochrones can be accurately reconstructedfrom a noncontact, nonexpandable, miniature multielectrode 9F catheterthat may, if desired, assume a curved geometry inside the cavity,without the need for expansion. The catheter need not be curved to workeffectively. Curvature simply enhances the results, as will bedemonstrated. The reconstruction is robust in the presence of errors,indicating feasibility of the approach in the clinical environment ofthe electrophysiology (EP) catheterization laboratory.

To obtain an accurate estimate of probe potentials, the forwardcomputation of probe potentials from the measured endocardial potentialswas performed with a very large number of “electrodes” (nodes) on theprobe surface. In the simulation, probes with 722 electrodes (30circumferential rows×24 electrodes/row+two end electrodes) were used.This is several times greater than the actual number of electrodes onthe probe used in the experiments. As confirmed by spherical modelsimulations, such a large number of electrodes (nodes) results in veryaccurate probe potentials. To study the effect of limited electrodedensity on the reconstruction, different subsets of electrodes (nodes)were selected on the surface of the simulated probe. The uniform spatialdistribution of electrodes over the probe surface was preserved. Theselected subset of probe potentials was then used in the inversereconstruction of endocardial potentials. This process was performed forprobes of different sizes and shapes.

The reconstruction of endocardial potential maps is performed in aquasi-static approach throughout the cardiac cycle, i.e., at a giventime instant, the endocardial map is computed from the probe potentialsrecorded at the same time. Once all endocardial potential maps arereconstructed, the data are reorganized according to electrode (node)and temporal electrograms depicting potential vs. time can bereconstructed for any position on the endocardial surface. In thisstudy, endocardial potentials and electrograms were computed for 50positions, where the tip electrodes of endocardial recording needleswere located, allowing a direct comparison of the computed electrogramswith the actual measured electrograms.

Endocardial isochrones, depicting the activation sequence of theendocardial surface, were constructed from the computed endocardialelectrograms. The time derivatives, dV/dt, of the inverselyreconstructed endocardial electrograms were computed, and the timeinstant associated with the maximum negative dV/dt (“intrinsicdeflection”) at a particular site was taken as the activation time ofthat site.

Over the entire endocardial surface, 50 electrograms were computed.Electrograms at 5 selected sites are shown in the results. FIG. 8 showsthe positions of these selected (numbered) sites. For both single anddual pacing cases, site 1 was chosen to be the earliest (one of theearliest, in the dual pacing case) measured endocardial activation site,while sites 2 to 4 are activated progressively later in time. Site 5corresponds to a site that is remote from the center of the cavity andtherefore far away from the catheter probe. The asterisks correspond topacing sites.

In the following description of experimental results, threerepresentative simulated catheter probes are compared in terms ofaccuracy of reconstructed endocardial electrograms and isochrones. Theprobes are: a cylindrical 7.6 mm diameter probe (generally too large forpercutaneous application), a cylindrical 3.0 mm diameter probe(equivalent to a 9F catheter that can be introduced percutaneously), anda 3.0 mm diameter probe bent in the cavity into a J-shape (close to thenatural shape assumed by a catheter in the cavity). Results withsimulated probes larger than the 7.6 mm cylindrical probe are verysimilar to those of the 7.6 mm probe. Initial results for a simulatedU-shaped catheter probe are also shown to demonstrate the effects ofdifferent curved catheter shapes on the reconstructions.

It should also be recognized that potential maps may also be generatedusing the system and method of the present invention. For example, FIG.29 shows measured and computed potentials for a single pacing site using122 and 62 electrodes, respectively, for the noted catheters. FIG. 30shows similar data for dual pacing sites.

FIG. 9 shows the reconstruction of endocardial electrograms fromdifferent probes containing 122 electrodes. The activation sequence isinitiated by pacing from a single site. Measured endocardialelectrograms at 5 selected sites are shown at the top, reconstructedelectrograms at corresponding sites are shown at the bottom. Thecorrelation coefficients (CC) between the measured and computedelectrograms are printed next to each computed electrogram. Over theentire endocardium, computed electrograms at 50 endocardial sitesresemble the measured electrograms very well. CC values at all sites arenear 1.0.

FIG. 10 shows reconstruction of endocardial electrograms from the probesusing a subset of 62 electrodes. The cylindrical 7.6 mm probe performsalmost as accurately as with 122 electrodes, except for the distant site(site 5). The cylindrical 3.0 mm and curved probes reconstruct 96% ofthe electrograms with CC greater than 0.90. There are discontinuities(“jagged” appearance or spikes) in some of the computed electrograms,which do not exist in the measured ones. Although the discontinuitiescause deterioration of the appearance of the electrograms, the generalshapes of the electrograms are preserved. Electrogram at the distantsite (site 5) reconstructed from the curved probe resembles the measuredelectrogram in terms of shape and amplitude. The computed electrogramsat a few nodes contain large spikes in certain time frames, the computedelectrograms resemble the measured ones very well except during thespikes. The spike can be removed by data interpolation.

FIG. 11 shows endocardial electrograms reconstructed from the probeswith 62 electrodes for a dual-site pacing protocol. The overallperformance of the J-probe is most acceptable, with high CC. The distantnode electrogram (site 5) is also reconstructed with very high accuracy.

Endocardial isochrones were constructed from both measured and inverselyreconstructed endocardial electrograms. FIG. 12 shows the isochronescomputed from the reconstructed electrograms of FIG. 9 and FIG. 10. Themeasured isochrone map is shown in the top panel and the computedisochrone maps in the bottom panels. The position of the earliestactivation time in the measured isochrone map is located at the pacingsite, indicated by an asterisk (*). The map shows that activation startsat the postero-lateral region and progresses to the anteroseptal regiontowards the base of the LV. The regions of both earliest activation andlatest activation in the measured isochrone map are accuratelyreconstructed in the computed isochrone map by the 7.6 mm cylindricaland curved catheter with either 122 or 62 electrodes. In contrast, thereconstructed isochrones using the 3.0 mm cylindrical probe with 62electrodes (second row) exhibit distortion of the earliest activationregion, and the latest region (red) divides into two regions. Theintermediate isochrones between the earliest and latest activation timesin the computed isochrone map closely resemble the measured isochronesfor all three probes. The reconstructed earliest activation time (17 ms)is accurate. The latest time of activation reconstructed by the curvedcatheter with 62 electrodes is 60 ms as compared to the measured valueof 63 ms.

FIG. 13 shows the activation sequences (isochrones) initiated by thedual-pacing protocol of FIG. 11. The measured isochrone maps (FIG. 13top panel) depict two distinct earliest activation regions at thevicinity of the two pacing sites. The earliest activation timesdetermined from the measured electrograms are 18 ms for the twoposterior pacing sites. The latest activation region is at theanteroseptal region close to the base of the LV, with activation time of55 ms. In the isochrone maps computed from the curved catheter with 122or 62 electrodes (bottom row), the two distinct earliest activationregions are correctly reconstructed. The earliest activation times inthe computed isochrone maps are exactly 18 ms. The region of latestactivation in the computed isochrone map is located at the anteroseptalregion near the base of the LV, in good agreement with its actuallocation in the measured isochrone map. In contrast, only one of the twoearly activation sites is present in the reconstructed isochronesobtained from the 7.6 mm and 3.0 mm cylindrical probes.

Geometrical errors can occur in determining the probe position insidethe ventricular cavity. The two most probable errors are shifts androtations of the probe as a rigid object. For the curved probe,twisting, i.e. rotation about the probe's own axis is also possible.These geometrical errors are illustrated in FIG. 14.

The effects of a 5-degree rotation error on electrogram reconstructionare shown in FIG. 15. All probes used are with 62 electrodes. For the7.6 mm cylindrical probe, 88% of all the electrograms are reconstructedwith CC greater than 0.95. The 3.0 mm cylindrical probe reconstructs 92%of the electrograms with CC greater than 0.95. Of the J-probereconstructed electrograms, 90% have CC greater than 0.95. It should benoticed that a uniform degree of angular rotation actually results indifferent position errors for electrodes on the different probes. The3.0 mm cylindrical probe experiences the smallest distance change, whileelectrodes on the J-probe “arm” experience the largest position error.This explains why the accuracy of J-probe reconstructions is sensitiveto this type of error. In contrast, the 3.0 mm cylindrical probetolerates the rotational error better than other disturbances.

FIG. 16 shows the isochrones computed from the electrograms of FIG. 15,which demonstrates the effects of a 5-degree angular rotation. FIG. 17shows the results for 10-degree rotation. Despite the fact that therotated J-probe has experienced a distance change, it still recoversacceptable activation regions. In the left column of FIG. 17, theJ-probe and the 3.0 mm cylindrical probe recover the earliest activationregion while the 7.6 mm cylindrical probe does not. In the right column,the J-probe recovers the earliest and latest activation regions with theleast pattern deformation compared to the other probes. FIG. 18 showsthe effects of probe rotation on a dual-pacing protocol. The 7.6 mmcylindrical probe recovers only one of the two pacing sites; the 3.0 mmcylindrical probe also reconstructs only one (the same) pacing site withgreater smoothing. The J-probe identifies the two simultaneous pacingsites with high correlation coefficients of 0.88 for 5 degree rotationand 0.92 for 10 degree rotation.

It has been determined that reconstruction quality under the disturbanceof rotation is related to the probe position inside the cavity, morespecifically, the position of the J-probe relative to the characteristicsites (pacing site, earliest or latest activation region) influences thereconstruction quality. One possible approach is to simply rotate thesame catheter probe in the cavity and record the potentials during twobeats, with different rotational positions. Another solution is tointroduce a second catheter probe into the cavity with an angle betweenthe two probes, to provide data from two orientations during a singlebeat. Also as will be shown later, increasing the arm length of theJ-probe to form a U-probe helps improve the accuracy of thereconstruction.

The effects of a shift in probe position on electrogram reconstructionare shown in FIG. 19. Overall, 68% of the recovered electrograms havecorrelation coefficients higher than 0.90. The 3.0 mm J-probe givesaccurately reconstructed electrograms of the early activation sites(column 1, 2, 3) and of the distant node (column 5). However, it failsto accurately recover the latest activation site (column 4), theelectrogram is severely distorted.

This is also reflected in the isochronal map of FIG. 20 left column,which is computed from the electrograms of FIG. 19 (2 mm shift). Theearly activation region is recovered with high accuracy by the 7.6 mmprobe and the J-probe. The 3.0 mm cylindrical probe reconstructs theearliest activations site, which has shifted in the lower rightdirection. The cylindrical probes perform better than the J-probe in thelatest activation region. 3 mm shift has the same effects on isochronereconstruction as shown in FIG. 20, right column. FIG. 21 shows the samesimulation for a dual pacing protocol. For 2 mm shift error, the 7.6 mmcylindrical probe reconstructs the earliest region with some distortion.The 3.0 mm cylindrical probe only recovers one of the two pacing sites.The J-probe reconstructs the two earliest activation sites, also withsome deformation of patterns in this region. Even for 3 mm shift error,the two earliest activation regions can be distinguished by the J-probe.

It has been determined that the tolerance of the reconstruction to probeshift errors is also related to the position of the probe inside thecavity. If a certain region of the endocardial surface is close to someprobe electrodes, the region tolerates better positional errors. Thereconstruction quality under the effects of shifting errors can also beimproved by using similar approaches as those suggested in the contextof the rotation errors.

FIG. 22 shows the electrograms reconstructed from a J-probe with 5degrees, 10 degrees and 15 degrees twist errors, and FIG. 23 shows thecorresponding isochrones. Electrograms display significant morphologicaldistortions in most of the nodes. For 5 and 10 degrees twist, even withmajor morphological changes in the electrograms, the isochrones stillrecover the earliest activation region and the latest activation region(although the latter is smoothed out). Under 15 degrees twist, thelatest activation region is completely smoothed out. For the dual-pacingprotocol, the J-probe with 5 degrees twist can still identify the twoearliest activation sites accurately. Under higher twist error, the twopacing sites merge together and can not be separated.

The J-probe used in this simulation study is characterized by arelatively short arm, as shown in FIG. 3. It serves to represent a largevariety of curved catheter probes with either different curvature orother shapes, such as “U”, or “O”, or any curved shape. In order toevaluate the effects of different catheter shapes on the reconstructionquality, simulations for a U-shaped catheter probe (FIG. 4) have alsobeen conducted. FIG. 24 shows the electrograms reconstructed from the3.0 mm probe, the J-probe and a 3.0 mm U-probe also with 62 electrodes.The U-probe has the same curvature as the J-probe. Note that thecomputed electrograms from the 3.0 mm cylindrical and J-probe are thesame as shown in FIG. 10. From the cylindrical probe to the U-probe, theaccuracy of the reconstruction progressively improves with the length ofthe “arm”. The U-probe reconstructs the electrograms with very highaccuracy, without any discontinuities or spikes. FIG. 25 left columnshows the isochrones computed from the electrograms of FIG. 24. Theimprovement in the latest activation region of the isochronesreconstructed by the U-probe is evident. The right column of FIG. 25shows the reconstructed isochrones from the three catheter probes withonly 42 electrodes. The 3.0 mm cylindrical and J-shaped probes fail torecover the earliest activation region, however, the U-probe stillaccurately reconstructs both the earliest and latest activation regions.Reconstructed isochrones for the dual pacing protocol from the catheterprobes are shown in FIG. 26. Only the U-probe, with either 62 or 42electrodes, recovers the two distinct earliest activation regionsaccurately. FIG. 27 shows the reconstructed isochrones from thecatheters under 5-degree rotation error. The performance of the U-probeis comparable or relatively better than the J-probe. Similarly, FIG. 28shows the reconstructed isochrones from the catheters under 2 mm shifterror. In the single pacing case (left column), the U-probe is the onlyone that recovers both the earliest and latest activation regions.

The results from the present study indicate that a noncontact,nonexpandable, miniature multielectrode catheter is useful for cardiacmapping. Although curving the catheter is not necessary to obtainrelatively accurate results, such curving results in improved results inmany respects. As is apparent from the above data, although a largenumber of electrodes is desirable when we consider the quality of theinverse reconstruction, it may raise other issues in design andmanufacturing of the probe and the data acquisition system. Thus, for aJ-probe, 60 probe electrodes or more is desirable because itreconstructed the endocardial electrograms and isochrones with goodaccuracy. However, the U-probe was found to tolerate reduced electrodenumber down to 42 very well.

The above description merely provides a disclosure of particularembodiments of the invention and is not intended for the purpose forlimiting the same thereto. As such, the invention is not limited to onlythe above described embodiments. Rather, it is recognized that oneskilled in the art could conceive alternative embodiments that fallwithin the scope of the invention.

1. A system for determining electrical potentials on an endocardial surface of a heart, the system comprising: a non-contact catheter probe having a surface and a terminal end portion adapted to be positioned in a cavity of the heart, the terminal end portion being adapted to be conformed into a first elongate shape and at least one second curved shape that includes a spiral shape, wherein the terminal end portion is conformed without expanding the terminal end portion; a plurality of electrodes disposed on the end portion of the probe, the electrodes being adaptable to measure electrical potentials in the cavity; imaging means for capturing geometric data on the probe and the endocardial surface; means for determining a geometric relationship between the probe surface and the endocardial surface based on the geometric data; means for generating a matrix of coefficients representing the geometric relationship between the probe surface and the endocardial surface; and, means for determining endocardial potentials based on catheter probe electrode potentials and the matrix of coefficients.
 2. The system as set forth in claim 1 wherein the second curved shape resembles one of a pigtail and a helix.
 3. The system as set forth in claim 1 wherein the probe includes means for conforming the terminal end portion of the probe to the first elongate shape while being positioned in the cavity and means for conforming the terminal end portion of the probe into the second curved shape once in the cavity.
 4. A system as set forth in claim 1, where the terminal end includes a cylindrical cross-section.
 5. A system as set for the in claim 1, where means for determining endocardial potentials include means for reconstructing endocardial potentials throughout the endocardial surface on a beat-by-beat basis.
 6. A system according to claim 1, further comprising at least one of: means for generating electrograms based on the determined endocardial potentials; and, means for generating isochrone maps based on the electrograms.
 7. A system for determining electrical potentials on an endocardial surface of a heart, the system comprising: a non-contact catheter probe having a surface and a terminal end portion adapted to be positioned in a cavity of the heart, the terminal end portion being cylindrical in cross-section and adapted to be conformed into a first elongate shape and at least one second curved shape that includes a spiral shape, wherein the terminal end portion is conformed without expanding the terminal end portion; a plurality of electrodes disposed on the end portion of the probe, the electrodes being adaptable to measure electrical potentials in the cavity; imaging means for capturing geometric data on the probe and the endocardial surface; means for determining a geometric relationship between the probe surface and the endocardial surface based on the geometric data; means for generating a matrix of coefficients representing the geometric relationship between the probe surface and the endocardial surface; means for determining endocardial potentials based on catheter probe electrode potentials and the matrix of coefficients; means for generating electrograms based on the determined endocardial potentials; and, means for generating isochrone maps based on the electrograms.
 8. The system as set forth in claim 7 wherein the second curved shape resembles one of a pigtail and a helix.
 9. The system as set forth in claim 7 wherein the probe includes means for conforming the terminal end portion of the probe to the first elongate shape while being positioned in the cavity and means for conforming the terminal end portion of the probe into the second curved shape once in the cavity.
 10. A system according to claim 7, further comprising at least one of: means for generating electrograms based on the determined endocardial potentials; and, means for generating isochrone maps based on the electrograms.
 11. A system for determining electrical potentials on an endocardial surface of a heart, the system comprising: a non-contact catheter probe means, having a surface and a terminal end portion, for position in a cavity of the heart, the terminal end portion being cylindrical in cross-section and adapted to be conformed into a first elongate shape and at least one second curved shape that includes a spiral shape, wherein the terminal end portion is conformed without expanding the terminal end portion; electrode means disposed on the end portion of the probe, for measuring electrical potentials; imaging means for capturing geometric data on the probe and the endocardial surface; means for determining a geometric relationship between the surface of the probe means and the endocardial surface based on the geometric data; means for generating a matrix of coefficients representing the geometric relationship between the surface of the probe means and the endocardial surface; means for determining endocardial potentials based on catheter probe electrode potentials and the matrix of coefficients; means for generating electrograms based on the determined endocardial potentials; and, means for generating isochrone maps based on the electrograms.
 12. A system according to claim 11, further comprising at least one of: means for generating electrograms based on the determined endocardial potentials; and, means for generating isochrone maps based on the electrograms. 